Hi Martha, wish I could help, but am new to ponding. I do know this though, to get an answer to that question you will probably have to be more specific. How big is the pond? Do you have a filter or aeration? Do you do water changes, and how much how often? What are the readings for ammonia, nitrate, nitrite, PH, etc.? Explain the dark, is it brown and cloudy or green? Hope this helps and you get some answers. Best of luck!

raise ph to about 7.8 add a uv steralizer,Barley straw extract And try to controal overfeeding fish

If you have adequate filtration, a new pond should cycle in a few months without the need of chemical additives or the cost of running electrical gizmos like UV sterilizers. After all, sooner or later, you will have to deal with all of the algae that the UV killed anyway.

What is the size of your pond, and how much filtration do you have?

I've had great luck changing out my filter pad for quilt batting. The filter pad wasn't finely woven enough to catch the floating gunk. I clean it out twice a day, rinsing the batting thoroughly; it gets completely saturated that quickly and could clog and cause the filter to burn out. After three days, I can now see the rocks at the bottom. Before, I couldn't even see one inch down.

How to make a pond clear - adequate filtration. No way around that.

Unfortunately, a lot of dealers and manufacturers chronically & seriously underestimate what their products will do - they will tell you that a pump or little filter box or something is "good for up to 1000 gallons" when at best it might work for 50 or 100 gallons. Helps to either find a KNOWLEDGEABLE pond store dealer or research via internet. Its a bad sign if at a pond or garden store you ask a question and they pick up the box to read what the label says.

How big is your pond? What everyone has said about filtration is bang on. You probably need far more than you currently have.

And I have had good luck with a UV sterilizer.

A couple of other things that I did that helped: I have a lighter floor, I put white stone at the bottom of the pond and this helps a bit. Also, you have to regular water changes, meaning that you need to take out of the pond some of the water. I have a 500 gallon pond and if we were talking aquarium maintenance, the rule of thumb would be a 20% water change every other week. Well, I cannot take out 100 gallons every other week but I probably take out 20-30 gallons every week. I have a separate pump for that and that is what I use to water my plants. I made my own soaker hose, so I just set it up before I get ready to mow the lawn...

I use Pond Cleaner Tablets that I buy at Home Depot. They're compressed barley flour. My water is brown, but clear and I can see the bottom of the pond. I also have only a mere three goldfish and a whole lot of plants including vigorously growing water hyacinth.

I use Muck Buster by Pond Builder (a powder) and then a weekly cleaner by Pond Builder. My pond is very clean. I have about 30 fish and various plants.